This application claims priority to Taiwan patent application Serial No. 090108363, filed Apr. 6, 2001.
The present invention is in association with a zero voltage, zero current switching power factor correction converter, and more particularly to a zero voltage, zero current switching power factor correction converter with low conduction loss and low switching loss.
As shown in FIG. 1, a single-phase boost converter for carrying out power factor correction is illustrated. In FIG. 1, when the main switch Sm turns on, the current will flow through two input diodes D3 and D2, boost choke L1 and main switch Sm; when the main switch Sm turns off, the current will flow through two input diodes D4 and D1, boost choke L1 and output diode Dm. Unquestionably, the power converter of FIG. 1 will result in a greater conduction loss.
Turning now to FIG. 2, another type of a single-phase boost converter for carrying out power factor correction is illustrated. Comparing to FIG. 1, though the power converter of FIG. 2 has a lower conduction loss, the rectifying diode of FIG. 2 has an inherent reverse recovery time (trr) problem, and a hyper fast recovery diode is required to be incorporated to reduce the switching loss for the main switches S1 and S2. Unfortunately, the hyper fast recovery diode has a significantly larger forward voltage (VF) than the input diodes of FIG. 1. Consequently, the power converter of FIG. 2 can not attain an anticipative performance. In other words, the power converter of FIG. 2 actually does not lead to the advantage of low conduction loss, and further the problems of electromagnetic interference (EMI) and radio frequency interference (RFI) still have not been addressed.
There is a tendency to provide a zero voltage, zero current switching power factor correction converter, which is operatively configured to drive the switches of the boost converter adapted for performing power factor correction to turn on and off in a zero voltage circumstances or in a zero current circumstances, and thereby lowering the conduction loss and the switching loss, miniaturizing the magnetic element, suppressing EMI and RFI and obtaining a better conversion efficiency.
An object of the present invention is the provision of a boost converter for carrying out the power factor correction, which has a lower conduction loss, lower switching loss, suppressed EMI, suppressed RFI, miniaturized magnetic element and an improved overall efficiency.
Another object of the present invention is the provision of a power factor correction converter which is operatively configured to drive the switches of the boost converter for use with the purpose of power factor correction to turn on and off in a zero voltage circumstances or in a zero current circumstances, and reducing the conduction loss caused by the current flowing through the switches, so as to optimize the overall performance of the power factor correction converter.
A first object of the present invention may be achieved by a boost converter which encompasses a resonant unit comprising a first switch, a second switch, a resonant circuit includes at least two energy storage elements, wherein the resonant unit is operatively configured to alternatively discharge electric energy from one of the energy storage elements to a load; and a boost unit comprising a boost choke for receiving an alternating current (AC) voltage, a rectifying circuit coupled between the boost choke and the resonant unit, a third switch and a fourth switch respectively connected across one of the energy storage elements.
With the intention of reducing the switching loss taken place at the instant that the switches are switching their on/off states, the resonant unit is operatively configured to respectively turn the first switch and the second switch on and off under a zero current circumstances, and the boost unit is operatively configured to respectively turn the third switch and the fourth switch on and off under a zero voltage circumstances.
In accordance with a first aspect of the present invention, the load is consisted of a first output capacitor, a second output capacitor and a resistor load (which may be a DC/DC converter), and the boost unit may optionally includes an inductor coupled between one side of the alternating current voltage and a circuit node of the fourth switch for reducing a common-mode noise of the boost converter. The resonant circuit includes an inductor, a first capacitor and a second capacitor. For simplicity, the output load xe2x80x9cresistorxe2x80x9d (which may be a DC/DC converter) is not shown in the drawings.
According to a first embodiment of the present invention, both the first switch and the second switch comprise a unidirectional switch. The unidirectional switch may be formed from a silicon-controlled rectifier or an insulated gate bipolar transistor with a relatively high collector-emitter reverse-biased voltage with gate opened (VCEO). An alternative for forming the unidirectional switch may comprise an insulated gate bipolar transistor or a metal-oxide-semiconductor field effect transistor (MOSFET)f. If the unidirectional switch is directed to an insulated gate bipolar transistor or a metal-oxide-semiconductor field effect transistor, a rectifying device such as a diode is required to couple in series with the second switch.
The rectifying circuit of the boost unit includes a first rectifier, a second rectifier and a third rectifier. In one preferred embodiment of the present invention, each of these rectifiers is implemented by an ultra fast recovery diode. In other preferred embodiments of the present invention, each of these rectifiers can be implemented by a MOSFET.
The boost converter of the present invention further comprises a first auxiliary rectifier and a second auxiliary rectifier, which can also be implemented by an ultra fast recovery diode.
Optionally, the boost converter of the present invention can further comprises a saturation inductor coupled between the inductor of the resonant circuit and the load for reducing a high-frequency ringing of the resonant circuit.
A second object of the present invention may be attained by a power factor correction converter, comprising a resonant unit which comprises a first switch, a second switch and a resonant circuit comprising at least two energy storage elements, wherein the resonant unit is operatively configured to alternatively discharge electric energy from one of the energy storage elements to a load; a boost unit comprising a boost choke for receiving an alternating current voltage, a rectifying circuit coupled between the boost choke and the resonant unit, a third switch and a fourth switch respectively connected across one of the energy storage elements; and a power factor correction controller which issues a first switch control signal to drive the first switch to turn on and off when a current flowing through the first switch is zero and issues a second switch control signal to drive the second switch to turn on and off when a current flowing through the second switch is zero, and issues a third switch control signal to drive the third switch to turn on and off when a voltage across the third switch is zero and issues a fourth switch control signal to drive the fourth switch to turn on and off when a voltage across the fourth switch is zero.
The power factor correction converter according to an exemplary embodiment of the present invention further includes a zero voltage detector which detects a voltage across the third switch and a voltage across the fourth switch, and issues a first control signal to drive the power factor correction controller to issue the third switch control signal when the voltage across the third switch is zero and issues a second control signal to drive the power factor correction controller to issue the fourth switch control signal when the voltage across the fourth switch is zero. More specifically, the resonant unit is operatively configured to respectively turn the first switch and the second switch on and off under a zero current circumstances.
The load according to a preferred embodiment of the present invention may comprise a first output capacitor, a second output capacitor and a resistor load. Optionally, the boost unit may further comprise an inductor coupled between one side of the alternating current voltage and a circuit node of the fourth switch for reducing a common-mode noise of the power factor correction converter. Moreover, the resonant circuit may comprise an inductor, a first capacitor and a second capacitor. The first capacitor and the second capacitor can be further combined into an equivalent capacitor.
More preferably, both the first switch and the second switch comprise a unidirectional switch. The unidirectional switch may be formed from a silicon-controlled rectifier or an insulated gate bipolar transistor with a relatively high collector-emitter reverse-biased voltage with gate opened (VCEO). An alternative for implementing the unidirectional switch may comprise an insulated gate bipolar transistor or a metal-oxide-semiconductor field effect transistor. If the unidirectional switch is directed to an insulated gate bipolar transistor or a metal-oxide-semiconductor field effect transistor, a rectifying device such as a diode is required to couple in series with the second switch.
The abovementioned rectifying circuit is formed from a first rectifier, a second rectifier and a third rectifier. Each of these rectifiers is comprised of an ultra fast recovery diode or a metal-oxide-semiconductor field effect transistor. Preferably, the boost unit may comprise a first auxiliary rectifier and a second auxiliary rectifier each of which is also implemented by an ultra fast recovery diode.
Optionally, the resonant unit further includes a saturation inductor coupled between the inductor of the resonant circuit and the load for reducing a high-frequency ringing of the resonant circuit.
Now the foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the accompanying drawings, wherein: